In recent years, along with the tough measures to protect the environment, the amount of dust recycled at iron works has increased. This dust is agglomerated to pellets of a diameter of 10 to 20 mm for use as blast furnace material. As the method for this, the cold pellet method using a hydrating binder is being industrially applied. A specific method of this cold pellet method is shown in FIG. 5. FIG. 5 is a view showing a conventional process of production of blast furnace-use cold pellets by yard curing. As shown in the drawings, a material comprised of dust produced from an iron works and/or fine powder ore is mixed by a kneader using a binder of Portland cement, then pelletized by a pan pelletizer, screened, then cured at a primary curing yard for about 3 days to obtain the initial strength, the cured pile is crushed using a bulldozer at that point of time, the crushed pellets are piled up again at the secondary curing yard and further cured for 1 week to obtain a predetermined strength, then the pellets are discharged and used at the blast furnace.
As an example, as disclosed in, for example, Japanese Patent Publication (A) No. 53-130202 (Patent Citation 1), a method of production of dust cold pellets is proposed which adjusts the particle size constitution of the formulation of the metal-containing carbon dust produced by an iron works to within a suitable range of distribution of particle size by selecting the ratio of the coarse particles and fine particles by means of mixing in powdered ore in accordance with need and which sets a suitable moisture content and adds cement or another binder for granulation. Further, as disclosed in Japanese Patent Publication (A) No. 63-83231 (Patent Citation 2), the method of production of non-fired agglomerated ore is proposed which blends granulated blast furnace slag fine powder and gypsum into a powder iron-containing material and pelletizes or agglomerates together the result to produce non-fired pellets or briquettes during which time the granulated blast furnace slag fine powder and gypsum are finely pulverized to a specific surface area of 4000 cm2/g or more, then blended in to the iron-containing material at a state of 40° C. or more in a ratio of 6 to 9%, an alkali activator is added, water kneaded in, and the result agglomerated, then the agglomerate is piled up in a yard, then cured while maintaining its temperature.
On the other hand, as the method for treating dust more simply than the above cold pellet method, there is the sintering-use minipellet method. FIG. 6 is a view showing a conventional process of production of sintering-use minipellets. As shown in this drawing, the minipellet method of mixing a material comprised of dust produced from an iron works and/or fine powdered ore by a kneader using a binder of bentonite, then using a pan pelletizer to form small-sized pellets of a diameter of 2 to 7 mm, screening them, then directly charging the pellets to a sintering machine without curing is also industrially applied. In the above example, for example, as disclosed in Japanese Patent Publication (A) No. 59-107036 (Patent Citation 3), non-fired minipellets for sintering materials have been proposed which are obtained by adding moisture to non-carbon-containing dust produced in the different processes of an integrated iron and steelmaking works and covering the surfaces by blast furnace primary dust.